1. Field of the Invention
The present invention relates to valve timing control systems that use a valve timing control device for controlling open-close timing of either one or both of an inlet valve and an exhaust valve in an internal combustion engine, and in particular, a valve timing control device (later described as intermediate position regulation valve timing control device) where regulation of relative turning is necessary at an approximately intermediate position within the controllable range when the internal combustion engine starts to run.
2. Description of the Related Art
In conventional valve timing control systems, a stopper pin for regulating housing and vanes is arranged in a valve timing control device, release of the stopper-pin is controlled by hydraulic pressure introduced into the valve timing control device, into advance-angle and retard-angle hydraulic pressure chambers, and the stopper pin release is controlled by using hydraulic pressure in an independent dedicated oil channel, distinct from the hydraulic pressure for controlling the relative turning position of the valve timing control device (for example, see Japanese Laid-Open Patent Publication 2001-227308, pages 6-7, FIG. 6).
A dedicated oil channel and a hydraulic control valve are provided in conventional valve timing control system in order to control regulation/release of relative turning of a valve timing control device by a regulator, however, because hydraulic pressure in an engine is generated by the engine's rotational output, for a certain period after the engine starts running, the hydraulic pressure is not supplied to the valve timing control device and the release of the regulator cannot be controlled.
Furthermore, during the normal running of the engine, the hydraulic pressure is applied steadily to the regulator via the hydraulic control valve and the dedicated oil channel, so that losses occur at hydraulic pressure input to these members while the engine is running, and due to oil leaks from various members.
Additionally, because the regulator engages with an engagement aperture when the hydraulic pressure becomes low due to unexpected decreases in engine rotation frequency during relative turning of the valve timing control device, the valve timing control device re-enters a regulated state.
Further, because cutting operations are required in order to install the dedicated oil channel and the hydraulic pressure control valve in the engine, and because a cleaning step in manufacturing this hydraulic system is necessary, the manufacturing process is complicated.